18-8型ステンレス鋼のプレス成形性におよぼすCuの影響

Abstract

The effects of the Cu content on the press formability as well as other machanical properties of 18-8 type stainless steels containing 0.06%C-16%Cr-7%Ni and 0.06%C-17%Cr-7%Ni were studied. The results are summarized as follows:(1) As the Cu content increases, both yield point and tensile strength decrease and show their minimum values at 3%Cu. However, no further change occurs beyond 3%Cu, while the total elongation rises with increase in Cu content, attains a maximum value at 2 or 3%Cu, and reversely decreases with a further increase in Cu content.(2) The work hardening coefficient (n-value) is lowered steeply with increase in Cu content up to 3% but gradually at more than 3%Cu. However, since the parabolic relationship between the true stress and the true strain is not applicable to some of the specimens even at a high strain level, it is not always suitable to evaluate the work hardenability from the n-value only.(3) The press formability evaluated by the conical cup value using either the flat headed punch or the rount headed punch is greatly improved with increase in Cu content, with a most favourable result at 2%Cu. But the increase in Cu content beyond 2% tends to deteriorate the press formability again, and at about 4%Cu the press formability of such low Cr, low Ni 18-8 type stainless steels results in the same degree as that of usual 18-8 type stainless steel, i.e. type 304.Thus changes in the conical cup value seem to be due to the difference in the shape of flow curves that depends on the Cu content.