TPT May 2014

Article

Shandong Province SiFang Technical Development Co, Ltd

Chemical composition (Mass fraction%)

C

Si

Mn

Cr

Ni

Mo

Cu

V

W Nb

Ti

P

S

GmbH & Co KG

1.60~ 2.80

≤ 1.2

≤ 1.2

8.0~ 28.0

0.5~ 3.5

0.5~ 2.0

≤ 1.0

≤ 1.0

≤ 1.0

appropriate quantity

appropriate quantity

≤ 0.04

≤ 0.04

Table 4: The chemical composition of high chromium alloy roll made in SDSF

3.7. High chromium alloy casting roll High chromium alloy casting roll has extensively applied to the production of steel pipe and cold roll formed steel, specially applying to the world’s advanced production lines. Since 1932, high chromium alloying roll was successfully developed by America, Germany, Japan, etc and was used in finishing rolling mills of hot rolling section steel mills, the front of roughing and finishing rolling steel of hot strip continuous rolling mills, roughing and finishing rolling of medium and heavy plate mills and finishing rolling mills of small size section steel and bar steel mills, the roll has higher wear resistance. At the Beijing international rolling steel conference 1989, the delegates attending the conference considered that high chromium roll used in cold and hot rolling strip mill and section steel rolling mill were successful [2] .Although our country was late starting in this respect, at present SDSF has successfully researched and developed the newhigh chromiumalloy casting roll which is suitable for the world’s advanced production lines for welding steel pipe and cold roll formed steel. Currently, the limit between high chromium iron and high chromium steel is not very clear. Although the iron and steel is usually differenced by 2% carbon content, the content of C for high C and high Cr steel is relaxed to 2.20-2.40%, such as China’s Cr12, Germany’s X210Cr12, America’s D3, Britain’s BD3 and Japan’s SKD11 [3] . The C content of high chromium iron чX22C, чX28 of Russia is 0.6-1.0% and 0.5- 1.6% separately [4] . High chromium alloy material is a kind of wide material in chemical composition limit; it has great difference in microstructure, hardness and toughness by different chemical composition and heat treated state.

The practice showed that it is very appropriate to decide chemical composition and heat treated process of roll by its working condition. Shandong Sifang Technical Development Co, Ltd (SDSF) has researched and developed a series of new high chromium alloy materials which possess different chemical compositions, different heat treating and different working process by studying the difference of roll under different working condition. ; micro hardness value is up to HV1800; microstructure is presented as discontinuous strip, lump, particle, chrysanthemum; the matrix is austenite and martensite; the combination between hardness and toughness is better; the macro hardness is up to HRC 50-65; the wear resistance, red hardness and speedily chilling and heating resistance are better in use; the aim of excellent property is achieved. Usual chemical composition is shown in table 4. The C and Cr element are the most important and most basic alloy elements in high chromium alloy material. The content of them decides the number of carbide, the relative number of M 7 C 3 carbide to total carbides, hardness, toughness and quenching degree of the material. The distribution of Mo in every phase of high chromium alloy material is about 50% into Mo 2 C; 25% into M 7 C 3 carbide. The hardness and wear resistance ability can be effectively increased and other 23% into matrix, the quenching degree is markedly increased. There is big bind capacity between W atomic and C atomic; it can enhance high temperature resolving stability of martensite so that the red hardness is enhanced. Under high temperature quenching a part of W carbide is melted into the matrix to enhance the quenching degree. Ni can not only force matrix and improve comprehensive property of material but can also increase quenching degree. Ti can refine eutectic structure to form stable Tic crystal nucleus. Through adding Nb the solidness phase – Nb(CN) particle, which possesses high hardness (HV2000), high melting point, regular shape, small particle size and uniform distribution, is precipitated in the matrix and it can effectively control solidification segregation of alloy, increase comprehensive properties and play the role of saving of Ni and Cr element. In the last 20 years the practice has proved that the series of high chromium alloy casting roll used in welding steel pipe and cold roll formed steel production can not only use for forming roll, sizing roll, strengthening roll but also extrusion roll, can not only use for cold environment but also hot environment. Their carbide is mainly M 7 C 3

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May 2014