the ce of 3 . 5 up to 4 . 0 may typically include from 3 . 0 wt % to 3 . 6 wt % of carbon , the remainder being substantially silicon . preferably the chromium content of the iron may be in the range from 0 . 5 wt % to 0 . 9 wt %. the cast iron composition may optionally contain copper in the range from 0 to 1 . 5 wt %, a preferred range being 0 . 5 wt % to 0 . 9 wt %. copper is used to counteract the effects of a lower ce to reduce shrinkage during solidification . copper also has the additional benefit of slightly increasing the hardness of the white iron regions . typical overall compositional ranges in wt % for cast iron materials used to make camshafts by the method of the present invention may comprise carbon : 3 . 0 - 3 . 6 , silicon : 1 . 5 - 1 . 8 , chromium 0 . 5 - 1 . 2 , molybdenum ; 0 - 0 . 25 , nickel ; 0 - 0 . 25 , copper : 0 - 1 . 5 , iron balance . typical preferred compositional ranges in wt % within the above overall range may comprise carbon 3 . 3 - 3 . 4 , silicon : 1 . 5 - 1 . 6 , chromium 0 . 7 - 0 . 8 , molybdenum 0 - 0 . 25 , nickel 0 - 0 . 25 , copper 0 . 6 - 0 . 8 , iron balance ; and carbon 3 . 15 - 3 . 35 , silicon 1 . 7 - 1 . 8 , chromium : 0 . 8 - 0 . 9 , molybdenum : 0 - 0 . 25 , nickel : 0 - 0 . 25 , copper : 0 . 6 - 0 . 8 , iron : balance . in the method according to the invention , the cooling rate is dictated ( as it was in the prior art method ) by the chills in the mould and by the mould material itself . given the controlled cooling rate , the depth of the white iron layer is now governed by the chemistry of the molten cast iron alone , principally by the and the nucleation is now fixed at an upper level which ensures that substantially all the residual liquid after solidification of the white iron solidifies as grey iron . nucleation now becomes , effectively , a fixed , easily controlled parameter which is set at a level to ensure that an excess of nucleant is present . according to a second aspect of the present invention there is provided a camshaft when made by the method of the first aspect of the present invention . in order that the present invention may be more fully understood , an example will now be described by way of illustration only with reference to the accompanying drawings , of which : fig1 shows a part of an iron -- carbon equivalent phase diagram in the region of the eutectic point ; fig2 shows a graph illustrating the effect of chromium content on the iron - graphite and iron -- iron carbide eutectic temperatures ; fig3 shows a graph illustrating the effect on eutectic temperatures of chromium segregation to the liquid during solidification ; fig4 shows a radial cross section through a mould cavity of a cam in a camshaft and adjacent metal chills ; and fig5 a and 5b shows two photomicrographs of sections through two cams , the one in fig5 a having been cast by a conventional method and the one in fig5 b by the method according to the present invention . it should be noted that in the phase diagram of fig1 the two values of eutectic temperatures illustrated are theoretical and the actual eutectic temperatures vary in practice depending upon the actual iron chemical composition with regard to both carbon equivalent elements and to alloying additions such as chromium . the effect of chromium on the two eutectic temperatures is illustrated in fig2 which shows the lowering of the iron - graphite eutectic temperature and the raising of the iron -- iron carbide eutectic temperature with increasing chromium content . this effect on eutectic temperatures becomes more pronounced as solidification proceeds and the chromium segregates preferentially to the liquid , resulting in the last liquid to solidify having a relatively higher chromium content , and therefore , a more marked effect on the shift of eutectic temperatures . the effect of progressively changing chromium content in the liquid as solidification proceeds is illustrated in fig3 where the two eutectic lines may intersect , resulting in the final solidifying liquid containing intercellular carbides . referring now to fig1 to 4 and the solidification of a prior art alloy ` a ` having a of 4 . 2 % will first be described followed by a description of the cooling of an alloy ` b `, having a of 3 . 7 %, by the method of the present invention . both the following descriptions will relate to solidification , depicted in fig4 of a cam 10 in a cavity of a sand mould 12 wherein there are relatively cold metal chills 14 , 15 adjacent the cam portion 16 and heel portion 18 . the mould 12 also has a parting line 20 . the molten metal 22 adjacent the chills 14 , 15 will experience a comparatively very high cooling rate compared with the metal 24 remote from the chills . the boundary between these two regions is indicated by the line 26 . it will be appreciated by those skilled in the art , however , that the line 26 is only generally indicative of the boundary between the region 22 which solidifies as white iron and surrounding the region 24 which solidifies as grey iron . it will be apparent to those skilled in the art that the metal immediately adjacent each side of the boundary 26 will experience substantially the same cooling conditions and that any boundary between the two constituents can be indicated only in general terms . molten iron is poured into the mould cavity at a pouring temperature which is substantially above the temperature of about 1160 ° c ., indicated at 40 in fig1 and , at which temperature the metal will begin to precipitate solid material in the form of austenite gamma phase . as the metal temperature falls rapidly in the region 22 adjacent the chill , insufficient time is available for carbon diffusion , substantial undercooling of the molten metal results which brings the temperature below the iron -- iron carbide eutectic temperature , indicated by line 42 , causing the metal in region 22 to solidify as white iron . the actual temperature of the line 42 will depend inter alia on the chromium content , the variation of the iron -- iron carbide eutectic temperature being indicated also in fig2 . the molten metal in region 24 , remote from the chills 14 , 15 is subjected to a lower cooling rate and the metal ideally possesses a level of nucleation which provides many sites for the growth of the typical graphite &# 34 ; rosettes &# 34 ; seen in grey iron , thus allowing little or no undercooling of the metal and causing the metal in the region 24 to solidify as grey iron . however , to ensure that the minimum specified depth of white iron is achieved in region 22 it is customary to err on the side of a lower level of nucleation than would cause all the metal in region 24 to solidify as grey iron . because the level of nucleation is , in any case , difficult to control accurately , the effect of this is often to cause the metal in region 24 to solidify as a mixture of grey and white iron . this is more pronounced with chromium present in the metal as the last liquid to solidify is relatively higher in chromium , owing to rejection from the solidifying metal , and causes the iron -- iron carbide eutectic temperature to rise relatively sharply as indicated in fig3 where the two eutectic temperature lines 42 , 46 may actually intersect . the last metal to solidify 48 may comprise intercellular carbides or a mixture of primary and intercellular carbides . the result is to produce a &# 34 ; core &# 34 ; of metal in the camshaft centre which is difficult , or impossible , to machine . reference to the cam shown on the left of fig5 shows the structure which is often produced by the conventional method ; the light areas are white iron and the dark areas are grey iron . it may be seen that the region corresponding to the grey iron region 24 has a &# 34 ; mottled &# 34 ; appearance indicating the presence of a relatively large proportion of white iron . referring now to the solidification of alloy ` b ` shown in fig1 and which alloy has a carbon equivalent of 3 . 7 %. solidification begins to occur at point 44 , approximately 1230 ° c ., at which temperature the austenite ( gamma phase ) begins to precipitate from the liquid ( it will be appreciated that the externally applied cooling conditions via the chills 14 , 15 are substantially the same as for alloy &# 34 ; a &# 34 ;). as cooling proceeds rapidly in the region 22 adjacent the chills 14 , 15 the proportion of the solid austenite phase to liquid increases until the eutectic temperature is reached . the cooling rate in region 22 is the structure determining factor and the austenite phase transforms to the white iron structure , the remaining liquid in region 22 undercools to below the iron -- iron carbide eutectic temperature , indicated by line 42 ; since insufficient time is available for carbon diffusion this liquid also solidifies as white iron . the slower cooling metal in region 24 , due to the fact that the poured metal charge possessed a level of nucleation which ensures solidification as grey iron , solidifies substantially as grey iron having significantly reduced proportion of included white iron . it is a comparatively simple and easily controlled matter to ensure that the nucleation level is high enough to ensure solidification substantially as grey iron in region 24 by using an excess of nucleating material . the high level of nucleation does not , however , prevent white iron forming in region 22 as this is governed by the cooling rate and the presence of sufficient austenite phase precipitating from the liquid during solidification which is initiated at a higher temperature . it has been found that camshafts produced by the method of the invention have given a significant improvement in the consistency obtained in the structure of the white iron region . this improvement in consistency may be illustrated by statistical analysis of rockwell c hardness measurements between the conventional method and the method of the present invention . rockwell c hardness measurements on a number of camshafts has given the data shown in the table below : ______________________________________ calculated mean cam capability nose hardness std indice cpk hrc deviation ( 45 hrc ) ______________________________________conventional 52 . 6 2 . 46 1 . 03methodpresent 52 . 8 0 . 92 2 . 8invention______________________________________ this data effectively demonstrates the method of the present invention to be much more controllable than the conventional method . a very important additional advantage of the method of the present invention is that by ensuring that substantially all the available carbon in region 24 is converted to the graphite form in grey iron , rather than as produced by the prior art method , then the cast iron composition in effect becomes sufficiently self - feeding , especially where there is also an addition of copper , not to need any other external feeders on the casting . although the invention has been described above with reference to a cam profile having a 360 ° white iron chill zone , the method of the invention is equally applicable to cams where a chill is applied only to the cam portion 16 , the heel portion 18 solidifying as grey iron .