ffmpeg transcode with parameter crf equals 0

When I use ffmpeg to transcode a video with :
ffmpeg -vcodec h264_cuvid -i 1.264 -vcodec h264_nvenc -rc vbr_hq -cq 0 -qmin 0 -qmax 0 -b:v 0 2.264

the psnr of the result is only 38.434320 , But when I use x264 its result is inf . Why the result of the transcode with crf=0 has such a low quality?