Study On Structure & Property Of Low-Alloyed Cylinder-Block

The 4DA1 engine is a neotype engine which will be put into operation recently by JAC automobile company. This paper is based on the casting of the cylinder-block, analyzing the main machined surface's surface hardness and key-part's body-strength, discussing the influential rule of Si, Cr, Sn's content on cylinder-block's structure and property.The hardness distribution of cylinder-blocks which have typical composition are all even relativily, ΔHBmax< 10HB,and makes it easy to carry on machine's process. body-strength are more than 200MPa.And high content of alloy elements caused hardness and strength increased apparently.High content of silicon caused graphite became coarsed, hardness and strength have a relatively deceased, but it has less influence on the shape of graphite and quantities of pearlite & carbide. The recruitment of graphite's length like lug is during 50 to 100um.the surface hardness of low silicon cylinder-block is during 194 HB to 217HB and high silicon cylinder-block is during 190 HB to 201HB . In addition,we found the hardness of cross section are all more even, after cylinder tube is dissected.Compared with the manner of addition Cr simply, add Cr with Sn can increase value of Brinell hardness and quanties of pearlite, but it has less influence on the upgrade of distance between commutator segments of pearlite. When the content of tin is increased from 0.069% to 0.091%,we found tin's content isn't has apparently influence on pearlite's refinement, the increasing scope of every part's surface hardness is during 2 HB to 20 HB, and the increasing scope of every part's body strength is during 5 MPa to 21 MPa.When we take the alloyed manner of added Cr with Sn, and the content of Cr is range from 0.245% to 0.390%,we found the pearlite's quantity wasn't increased and distance between commutator segments also hadn't upgraded, but the hardness and strength have a Up-trend totally. and not only surface hardness but also cross-sectional hardness all rised evenly, and during the scope of 10 to 25HB.The rising amplitude of strength is very large, most parts increased 20 to 30 MPa, especially the base plate which is increased 53MPa.The strength of cylinder-block with low-alloyed Cr is more than 220MPa,withmiddle's is more than 230MPa,with high's is more 255MPa.Condering the manufacturing property and the demand of body-strength totally, this type of cylinder-block should have the composition as follows: C=3.2—3.4%, Si=l.8 — 2.0%, Mn=0.7~0.9%, S=0.06~0.15%, P<0.06%, Cr=0.2~0.3%, Sn=0.05~0.10%o...