The Importance of MnS Inclusions on Hot Shortness of Cu-Containing Steels

Abstract

A novel approach on the problem of hot cracks in Cu-containing steels is proposed to prevent the hot shortness. Cu-containing steels have been hot tensile tested to failure in argon or vacuum at different cooling rates and temperatures, followed by Scanning Electron Microscopy. EDX analysis both in fractures and cross section show that inclusions are very important in causing the Cu concentration. Although CuS precipitates slightly deteriorate the hot ductility between the Ae 3 and Ar 3 temperatures, the Cu concentration around inclusions can highly contribute to hot shortness by the formation of Cu-containing liquid phase. Laboratory results combine with thermodynamic calculations show that a Cu-containing liquid associated with inclusions at %1200 8C is clearly the cause of the hot shortness. A distinction of hot ductility and hot shortness is proposed, concerning to their very different cracking mechanisms. The interpretation of the hot tensile test for each testing condition and temperature range is discussed. It is concluded that the oxidation is not the principal cause of the increase of Cu concentration, so its importance is relative in the laboratory assessment of hot cracking. Consequently, inclusions cannot be ignored in assessing and preventing the hot shortness, and commercial implications are drawn from the results.

ADVANCES IN THE ASSESSMENT OF HOT CRACKING OF Cu-CONTAINING STEELS

“…Once that statement is accepted, it is then clear that oxidizing is an important condition to simulate the problem of hot shortness. However, recent investigations [10,13] show that effects of copper and nickel are not exactly like previously reported [7]. Results to be published [5] show that the problem of hot shortness can be more serious.…”

“…We contend that hot shortness actually results from the melting of segregated metallic copper at higher temperatures (above Ae3) of hot-deformation, causing cracking, but the copper segregation is not consequence of oxidation as it is proposed by the current literature. Recent works [5,6] proposes a novel approach for the Cu segregation being related to the presence of inclusions which is the principal cause of the hot shortness. The same work reports that within the bulk, copper segregates to MnS inclusions exacerbating the problem of segregation.…”

Copper‐Alloyed Precipitation‐Hardenable‐Ferritic‐Pearlitic Steel for Energy‐Efficient and Distortion‐Reduced Production of Cold‐Formed, High‐Strength Structural Components

“…Since copper is relatively stable to oxidation, the copper accumulates in the surface layer of steels during oxidation in the furnace atmosphere. The result is the formation of a molten copper phase that penetrates into the grain boundaries and can thus lead to intergranular cracks during forming . The SHS effect can be effectively mitigated by the addition of various alloying elements.…”

“…The same applies to forming at very high speeds, where the critical stress for embrittlement by the liquid copper is increased. In addition, even a small amount of water in the furnace atmosphere can significantly accelerate the hot brittleness and should therefore be avoided . A new concept for a Precipitation‐Hardenable‐Ferritic‐Pearlitic steel (PHFP steel) and the associated production technology aims to exploit the positive effects of copper.…”

“…The result is the formation of a molten copper phase that penetrates into the grain boundaries and can thus lead to intergranular cracks during forming. [2,[20][21][22][23][24] The SHS effect can be effectively mitigated by the addition of various alloying elements. The literature mainly refers to a combination of nickel and silicon.…”